Fuel treatment additives have been developed in recent years which modify diesel fuels to prevent freezing and to improve efficiency, power and environmental characteristics. Usually, such additives are mixed with the fuel in a ratio of approximately one part per thousand or less, perhaps as little as one part in ten thousand. For example, additives made by Parrish Chemical Company of Provo, Utah, and distributed under the trade names FERROX and FPC-1 are catalytic agents which, in concentrations of as little as one part in 5,000, improve combustion efficiency and reduce particulate carbon exhaust emissions. While higher concentrations are tolerable, little benefit is gained. Since all such additives are relatively expensive, It is desirable to maintain a mixture concentration scarcely greater than the effective minimum.
In the most basic method of application, the fuel treatment is dispensed manually by simply measuring out an appropriate quantity of additive for the desired concentration and pouring it into the tank. This works particularly well in a fixed base operation where tankage is maintained for fueling a number of locally operated vehicles and supervision is close at hand. Vehicle operators not having such supply systems, and long haul operators, must treat their fuel at each refueling stop. Additives are highly concentrated and generally disagreeable or even dangerous to handle. Inclement weather, urgent schedules, human error and careless neglect also conspire against the efficacy of manual dispensing procedures. The benefits of a consistent fuel treatment program are compelling however, and various means have been evolved in an attempt to resolve the implementation problem. Among these is Dudrey, who in his U.S. Pat. No. 4,253,436, has disclosed a manually controlled system wherein, after refueling, the operator makes a control panel input of the fuel quantity added to initiate an electrically operated synthesis of the manual procedure. After the fuel quantity is entered, a dispensing pump is caused to run for the period of time needed to inject an appropriate amount of additive separately into each fuel tank. The human problems of error and careless neglect, according to the teaching of Dudrey, are addressed only through "later checking by supervisory personnel for determining that the operator/driver caused the liquid additive to be added to the vehicle fuel."
As a general rule, diesel trucks have saddle tanks on either side, interconnected with a tank level balance line. The tanks have separate fillers, since the cross-flow capacity of the balance line is much less than the refueling rate. Usually only the tank on the driver's side has a fuel level gauge sensor and, as fuel is used, the balance line distributes the remaining fuel equally between tanks. Modest errors in the fuel level may be sensed when driven or parked on sloping terrain, but normally such slopes do not exceed 1:20 and the sensor is located more or less centrally in the tank so that such errors are not of significant magnitude. The single tank sensor is unreliable only during refueling, when one side or the other is being filled rapidly. Another potential source of sensor error is wave action or sloshing of the fuel. To minimize this effect, the fuel tanks are baffled and the gauge circuit is electrically damped to further stabilize the indicated fuel level.
U.S. Pat. No. 4,621,593 by Rao, et al, discloses a system for dispensing an exhaust deposit treatment additive by an automatic cycle, initiated by the removal of the fuel filler cap and shut down by replacement of the cap. The change in resistance of a fuel level sensor is used to compute the number of pulses of a diaphragm type pump needed to dispense additive for treatment of the added fuel. The accuracy of the computed pulse count is dependent upon the accuracy of "snapshot" fuel level gauge readings and may be adversely affected by wave action or other transient anomalies. In inclement weather, the driver may elect to fill only one saddle tank, on the sheltered side of the truck, causing a major gauge errors until the balance line has time to equalize tank levels. To cope with such inaccuracies, the system must be calibrated to supply a quantity of additive well in excess of the ideal minimum. Additionally, a fuel cap switch or any such mechanical interface device can be unreliable, particularly with field installation of a kit.
Similar single tank and multiple tank refueling sequences are practiced when diesel fuels are used in stationary power, maritime power and industrial heating applications.
A primary object of the present invention is therefore, to provide a fully automatic fuel additive dispensing system which performs without supervision. A second object is to provide such a system capable of compensating for the human and physical variables of refueling, so as to accurately maintain a predetermined minimum additive concentration. A third object is to provide an additive dispensing system as a universally applicable unit, requiring only electrical and fluid connections for installation.
The present invention accomplishes these objectives with a system comprising the existing fuel tank and fuel level sensor, an additive tank, a fixed delivery rate additive transfer plump and a microprocessor programmed for fuel level and rate-of-change logic. The additive pump cycle is controlled by the microprocessor according to the fuel level logic. Fuel level is read on a continuing schedule at fixed "point-in-time" intervals, with the accuracy of each such point-in-time reading preferably being enhanced by averaging several readings taken during a brief period. Then, the micro-processor is programmed to compare consecutive point-in-time readings, evaluate change and rate of change of the fuel level to identify the beginning and end of a refueling event, and to initiate an appropriate additive dispensing sequence.